NESC Article 410

The National Electrical Safety Code® (NESC®), used throughout the U.S., gives guidance on safeguarding employees working on electrical supply and communication lines during design, installation, operation, and maintenance. The NESC® is a performance code that deals with the safety of electrical supply lines, power-related telephone and cable TV lines, and rail power and signal installations. Among other topics, the standard addresses protective clothing.

“The employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure greater than 2 cal.cm2 exists, the employer shall require employees to wear clothing or a clothing system that has an effective arc rating not less than the anticipated level of arc energy.”

The standard also states:

“When exposed to an electric arc or flame, clothing made from the following materials shall not be worn: acetate, nylon, polyester, or polypropylene.

The effective arc rating of clothing or a clothing system to be worn at voltages 1000V and above shall be determined using Tables 410-1 and 410-2 or by performing an arc hazard analysis.

When an arc hazard analysis is performed, it shall include a calculation of the estimated arc energy based on the available fault current, the duration of the arc (cycles), and the distance from the arc to the employee.

EXCEPTION 1: If the clothing required by this rule has the potential to create additional and greater hazards than the possible exposure to the heat energy of the electric arc, then clothing with an arc rating or arc thermal performance value (ATPV) less than that required by the rule can be worn.

EXCEPTION 2: For secondary systems below 1000V, applicable work rules required by this part and engineering controls shall be utilized to limit exposure. In lieu of performing an arc hazard analysis, clothing or a clothing system with a minimum effective arc rating of 4 cal/cm2 shall be required to limit the likelihood of ignition.

NOTE 1: A clothing system (multiple layers) that includes an outer layer of Flame Resistant material and an inner layer of non-Flame Resistant material has been shown to block more heat than a single layer. The effect of the combination of these multiple layers can be referred to as the effective arc rating.

NOTE 2: It is recognized that arc energy levels can be excessive with secondary systems. Applicable work rules required by this part and engineering controls should be utilized.”